BOTH INTERNATIONAL & INLAND Five or more short blasts on a vessel's whistle indicates that she is __________.

Correct Answer: Option B — in doubt that another vessel is taking sufficient action to avoid a collision

Under Inland Navigation Rules, for the condition where 'Five or more short blasts on a vessel's whistle indicates that she is', the correct requirement is: 'in doubt that another vessel is taking sufficient action to avoid a collision'. This standard ensures clear navigational intent and collision avoidance.